JP4715358B2 - Alloy steel powder for powder metallurgy - Google Patents

Description

  The present invention relates to an alloy steel powder suitable for use in powder metallurgy.

Powder metallurgy technology makes it possible to produce a part having a complicated shape with high dimensional accuracy in a shape very close to the product shape (so-called near net shape), and to greatly reduce the cutting cost. For this reason, powder metallurgy products are used in various fields as various machines and parts.
Recently, high strength is strongly required as a physical property of iron-based powder metallurgy products in order to reduce the size and weight of parts.

  Iron-based powder compacts for powder metallurgy are generally mixed with iron-based powders, alloy powders such as copper powder and graphite powder, and lubricants such as stearic acid and lithium stearate. This is filled in a mold and press-molded for manufacture. Iron-based powders are classified into iron powder (for example, pure iron powder), alloy steel powder, and the like, depending on the components. Moreover, in the classification according to the manufacturing method, there are atomized iron powder, reduced iron powder, and the like. In these classifications, iron powder is used in a broad sense including alloy steel powder.

As the density of the molded body obtained by a normal powder metallurgy process, 6.6 to 7.1 Mg / m ³ is common. These iron-based powder compacts are further subjected to a sintering treatment to obtain sintered bodies, and further subjected to sizing and cutting as necessary to obtain powder metallurgy products. If higher strength is required, carburizing heat treatment or bright heat treatment may be performed after sintering.
In order to improve the tensile strength of powder metallurgy products, high alloying is considered, but the problem is that the alloy steel powder as a raw material hardens, compressibility decreases, and the equipment burden in press molding increases. . In addition, the decrease in compressibility of the alloy steel powder offsets the increase in strength through a decrease in the density of the sintered body. Therefore, a technique for increasing the strength of the sintered body while suppressing the decrease in compressibility as much as possible is required.

As a technique for increasing the strength of a sintered body while maintaining compressibility, an alloy element such as Ni, Cu, or Mo that improves hardenability is generally added to an iron-based powder.
As an effective element for this purpose, for example, in Japanese Examined Patent Publication No. 63-66362, Mo is added as a pre-alloying element to iron powder within a range that does not impair compressibility (Mo: 0.1 to 1.0% by mass). By diffusing and adhering Cu and Ni in the form of powder to the particle surface, both compressibility during compacting and strength of the sintered member are achieved.

  JP-A-61-130401 discloses an alloy steel powder for powder metallurgy for high-strength sintered bodies in which two or more kinds of alloy elements, particularly Mo and Ni, or further Cu are diffused and adhered to the surface of steel powder. Has been proposed. In this technology, it has been proposed to control each diffusion adhesion element so that the diffusion adhesion concentration with respect to fine powder having a particle diameter of 44 μm or less falls within the range of 0.9 to 1.9 times the diffusion adhesion concentration with respect to the entire steel powder. It is said that the impact toughness of the sintered body is ensured by this limitation to a relatively wide range.

However, Ni and Cu are disadvantageous elements from the viewpoint of environmental response and recyclability in recent years, and it is desirable to avoid their use as much as possible.
Mo-based alloy steel powders that do not contain Ni or Cu as the main alloying element have been proposed. For example, in Japanese Examined Patent Publication No. 6-89365, in order to promote sintering by forming an α single phase with a high self-diffusion rate of Fe, Mo, which is a ferrite stabilizing element, is preliminarily in a range of 1.5 to 20% by mass. Alloy steel powders included as alloys have been proposed. This alloy steel powder is homogeneous and stable by adapting the particle size distribution to the process of pressure sintering to obtain a high-density sintered body and by not using a diffusion adhesion type alloy element. The organization is said to be obtained. However, the amount of Mo added is relatively high at 1.8% by mass or more in the actual disclosure, and the compressibility is low, so that there is a disadvantage that a high molding density cannot be obtained. For this reason, when a normal sintering process (sintering without pressing) is applied, only a low sintering density can be obtained.

Similarly, as an alloy steel powder for powder metallurgy containing Mo as a main alloy element, there is a technique disclosed in Japanese Patent Laid-Open No. 2002-146403. This technology proposes an alloy steel powder in which Mo: 0.2-10.0 mass% is diffused and adhered to the surface of an iron-based powder containing Mn of 1.0 mass% or less, or less than 0.2 mass%, and Mo as a pre-alloy. Is. This alloy steel powder is said to be excellent in compressibility and to obtain a sintered part having high density and high strength. However, this steel powder is adapted to a powder metallurgy process including recompression and re-sintering of a sintered body. Therefore, the above-described effects are not so much exhibited by a normal sintering method.
On the other hand, Japanese Patent Publication No. 7-51721 discloses an iron alloy powder (alloy steel powder) in which Mo is added to iron powder as a prealloy element in the range of 0.2 to 1.5 mass% and Mn in the range of 0.05 to 0.25 mass%. Has been. This alloy iron powder is a low alloy and is said to have a relatively high compressibility during pressure forming, and a high-strength sintered body is obtained. However, the present inventors have newly found out that there are the following problems. At the sintering temperature (usually 1120-1140 ° C) of the mesh belt furnace generally used for powder metallurgy, the progress of sintering between particles is not sufficiently promoted, and the sintering neck part (sintering reaction start part) : Later described) is insufficiently strengthened, so that a sufficiently high strength cannot be obtained.
Japanese Patent Publication No.63-66362 JP-A-61-130401 Japanese Patent Publication No. 6-89365 JP 2002-146403 A Japanese Patent Publication No. 7-51721 Japanese Patent Laid-Open No. 2001-181701 JP 2002-327204 A

  The present invention overcomes the above-mentioned problems of the prior art and increases the strength even at relatively low temperature sintering while maintaining a high density of the sintered body (ie, compressibility of the alloy steel powder). An object of the present invention is to provide an alloy steel powder for powder metallurgy.

The present invention relates to an iron-based powder containing , as a pre-alloy , an alloy element X that is one or more of Al, Si, P, Ti, V, Zn, Sn, and W, the balance being Fe and inevitable impurities An alloy steel powder for powder metallurgy in which a powder containing an alloy element Y which is one or more of Al, Si, P, Ti, V, Cr, Zn and Sn is attached to the surface of The pre-alloy amount (mass%) of the alloy element X of the iron-based powder is Al: 0.05 to 0.6, Si: 0.1 to 1.5, P: 0.05 to 0.3, Ti: 0.05 to 0.4, V: 0.05 to 1.0 , Zn : 0.1 to 5, Sn: 0.1 to 1.5, W: 0.1 to 5 were satisfied, and the average content (mass%) of the alloy element Y was Al: 0.05-2, Si: 0.05-6, P: 0.05-2, Ti: 0.05-2, V: 0.05-3, Cr: 0.05-20, Zn: 0.05-5, Sn: 0.05-8 are satisfied, and the alloy element Y is further formed on the surface layer of the iron-based powder. Concentration (mass%) of Al: 1 or more, Si 2 above, P: 0.5 or more, Ti: 0.5 or more, V: 2 or more, Cr: 13 or more, Zn: 7 or more, Sn: is on 2 or more is a powder metallurgical alloy steel powder high density portion is present.

In the alloy steel powder for powder metallurgy according to the present invention, it is preferable that the powder containing the alloy element Y is diffusely adhered. Alternatively, it is preferable that a powder containing the alloy element Y is attached to the binder.
Moreover, it is preferable that a high concentration part exists in 1 to 50% of range of the cross-sectional area of the alloy steel powder for powder metallurgy .

  The alloy steel powder for powder metallurgy according to the present invention is suitable as an alloy steel powder for powder metallurgy used as a raw material for a high-density sintered member having a high density of a sintered body. High strength can be obtained in the sintered body even when the treatment is performed at a relatively low sintering temperature, such as when sintered in a mesh belt furnace.

Hereinafter, the alloy steel powder for powder metallurgy according to the present invention will be described in more detail with reference to the drawings.
As schematically shown in FIG. 1 (a), the particles of alloy steel powder 4 for powder metallurgy of the present invention adhere to the portion 3 where the particles of Y-containing powder 2 and the particles of iron-based powder 1 are in contact. Yes. For example, in the case of diffusion adhesion, a part of the alloy element Y in the particles of the Y-containing powder 2 diffuses into the particles of the iron-based powder 1 (hereinafter referred to as partial diffusion), and the surface of the particles of the iron-based powder 1 (Hereinafter referred to as diffusion adhesion).

Depending on the manufacturing method, the Y-containing powder 2 may have a particulate original shape as shown in FIG. 1 (a), or the Y-containing powder 2 may be crushed as shown in FIG. 1 (b). In some cases, these forms are referred to as particles.
Hereinafter, unless otherwise specified, the iron-based powder refers to the iron-based powder 1 to which the Y-containing powder 2 is attached as defined in FIG. 1 and the iron-based powder as a raw material thereof, and the distinction between the two is as follows. It shall be done as necessary. Further, unless otherwise specified, the alloy steel powder refers to the powder of the present invention consisting essentially of four alloy steel powders defined in FIG. 1 and having two Y-containing powders adhered to one iron-based powder particle. And

Next, an example of the manufacturing method of the alloy steel powder for powder metallurgy of this invention is demonstrated.
As shown in the manufacturing process example (block diagram) of FIG. 2, first, an iron-based powder (a) (an iron-based powder as a raw material) containing a predetermined amount of an alloy element Y as an alloy component (ie, as a pre-alloy) in advance. Y raw material powder (b), which is a raw material for Y-containing powder, is prepared.
As the iron-based powder (a), so-called atomized iron powder is preferable. Atomized iron powder is an iron-based powder obtained by spraying molten steel with alloy components adjusted according to the purpose with water or gas. The atomized iron powder is usually subjected to a treatment for reducing C and O from the iron powder by heating in a reducing atmosphere (for example, a hydrogen atmosphere) after the atomization. However, it is also possible to use so-called “as-atomized” iron powder that is not subjected to such heat treatment as the iron-based powder (a) as a raw material of the present invention.

In addition, so-called reduced iron powder, electrolytic iron powder, pulverized iron powder, and the like can be used without problems as long as the components are suitable.
As the Y raw material powder (b), the target Y-containing powder itself may be used, or a compound of the alloy element M that can be reduced to the Y-containing powder may be used. However, any metal elements other than the alloy elements Y and Fe are not substantially contained.

As the powder containing the alloy element Y, a pure metal powder of the element Y or a commercially available alloy powder can be preferably used.
Further, as the compound of the alloy element Y, oxides, carbides, sulfides, nitrides, or composite compounds thereof can be used. Metal salts of alloy element Y can also be used. However, it is preferable to use an oxide from the standpoint of availability and ease of reduction reaction. The compound of the alloy element M is used in the form of powder or powdered by treatment such as mixing and reduction. The main component of the Y-containing powder obtained by reducing the alloy element Y compound is a pure metal of element Y or a Y-Fe alloy.

In any case, as a means for pulverizing the raw material of the alloy element Y, any method such as pulverization or atomization treatment may be used.
Next, the iron-based powder (a) and the Y raw material powder (b) are mixed (c) at a predetermined ratio. For the mixing (c), any applicable method (for example, a Henschel mixer or a corn mixer) can be used.

First, the manufacturing process for diffusing and adhering the Y-containing powder to the iron-based powder will be described below.
When diffusing and adhering the Y raw material powder (b), spindle oil, etc. should be added in the range of 0.1% by mass or less in order to improve the adhesion between the iron base powder (a) and the Y raw material powder (b). Is also possible. In order to exert the effect of the spindle oil, addition of 0.005% by mass or more is preferable.
When diffusion adhesion is performed, this mixture is kept at a high temperature, and the alloy element Y is diffused into the iron at the contact surface between the iron-based powder (a) and the Y raw material powder (b) and bonded (heat treatment (d) Thus, the alloy steel powder (e) for powder metallurgy of the present invention can be obtained.

As the atmosphere of the heat treatment (d), a reducing atmosphere is suitable, and a hydrogen-containing atmosphere, preferably a hydrogen atmosphere is particularly suitable. Note that heat treatment may be applied under vacuum. A suitable temperature for the heat treatment (d) is in the range of 800 to 1000 ° C.
When atomized iron powder is used as the iron-based powder (a), the content of C and O is high, so C and O can be reduced by making a reducing atmosphere in the heat treatment (d). Is preferred. This reduction action makes the iron-based powder surface active, and adhesion due to diffusion of the Y-containing powder surely occurs even at a low temperature (about 800 to 900 ° C.). Therefore, as-atomized iron powder is suitable as the iron-based powder (a) used as a raw material for the alloy steel powder for powder metallurgy of the present invention, compared to atomized iron powder that has been subjected to treatment for reducing C and O in advance. . In addition, about suitable content of C and O in the alloy steel powder for powder metallurgy will be described later together with other components.

By the above method, the alloy steel powder for powder metallurgy of the present invention schematically shown in FIG. 1 is obtained.
Needless to say, when the Y-containing powder 2 is used as the raw material powder of the alloy element M, diffusion adhesion occurs between the Y-containing powder 2 and the iron-based powder 1.
On the other hand, when a compound of the alloy element Y is used as the raw material powder of the alloy element Y, diffusion adhesion occurs between the contained powder 2 and the iron-based powder 1 even though the compound of the alloy element Y is reduced. When an oxide powder of alloy element Y is used as a specific example, the oxide is reduced to the form of Y-containing powder 2 (metal powder of alloy element Y) on the surface of iron-based powder 1 in this heat treatment step. As a result, as in the case where the Y-containing powder 2 is used as the raw material powder, diffusion adhesion occurs between the reduced Y-containing powder 2 and the iron-based powder 1.

From the viewpoint of the degree of Y adhesion, it is preferable to use a compound of the alloy element Y rather than using the Y-containing powder 2 as the raw material powder of the alloy element Y. This is because the surface of the Y-containing powder 2 reduced in the heat treatment step becomes active against the diffusion reaction, so that the degree of Y adhesion to the iron-based powder 1 is improved.
Alternatively, as shown in FIG. 2, the M-containing powder 2 is adhered to the surface of the iron-based powder 1 using a binder (hereinafter referred to as binder adhesion (f)) without performing diffusion adhesion by heat treatment (d). May be.

  The binder is not limited to a specific material, but as such a binder, metal soaps such as zinc stearate and calcium stearate, and amide waxes such as ethylene bisstearamide and stearic acid monoamide are conventionally known. A binder can be used. In particular, each of the above-mentioned binders is suitable because it has a lubricating function, but a binder having a low lubricating function such as PVA (polyvinyl alcohol), vinyl acetate ethylene copolymer, and phenol resin can also be applied. Here, the lubrication function is a function at the time of pressure molding, and refers to a function such as an improvement in the density of the molded body by promoting the rearrangement of powder and an improvement in the extraction property.

  These binders can be adhered to the surface of the iron-based powder 1 by heating and melting to the melting point or higher (including the co-melting point), but the adhesion by the binder is not limited to this method. For example, a means may be used in which the binder component is dissolved in a solvent and applied to the iron-based powder 1 and the Y-containing powder 2 to adhere both, and then the solvent is volatilized. In the case of using the above-mentioned binder such as metal soap, it is preferable to contain a binder having a melting point of about 80 to 150 ° C., and to heat the Y-containing powder 2 to a temperature higher than these melting points.

  When the heat treatment (d) (including diffusion adhesion treatment) is performed as described above, the iron-based powder 1 and the Y-containing powder 2 are usually sintered and solidified. Classification and further annealing as necessary to obtain alloy steel powder (e) product for powder metallurgy. In addition, the surface fatigue strength obtained by pressing and sintering alloy steel powder for powder metallurgy may be better produced by diffusion adhesion than that produced by binder adhesion. Many.

On the other hand, the alloy steel powder for powder metallurgy (e) produced by adhering to the binder does not need to be crushed and classified. Therefore, it is advantageous that the production cost is lower by the binder adhesion.
As a method for attaching the Y-containing powder 2 to the surface of the iron-based powder 1, either diffusion adhesion or binder adhesion may be appropriately selected according to the use and specification of the alloy steel powder for powder metallurgy.

Further, a part of the Y-containing powder 2 added or generated for the purpose of adhesion may remain in the alloy steel powder 4 in a state where it is not adhered to the surface of the iron-based powder 1 (so-called free state). Although it is preferable that the amount of the Y-containing powder 2 in the free state is small, the adverse effect is limited as long as it is an amount that can be generated by the normal adhesion treatment as described above.
The attaching means is not necessarily limited to the means described above, and any means can be applied as long as the degree of adhesion is comparable to the above means.

Next, the reason for limiting the amount of alloy elements in the alloy steel powder 4 for powder metallurgy according to the present invention will be described.
In the alloy steel powder 4 for powder metallurgy according to the present invention, the content of the alloy element X contained in the iron-based powder 1 as a pre-alloy (that is, as an alloy component in advance) is the powder metallurgy when the alloy element X is contained as a pre-alloy. It is the following concentration range A with respect to the mass of the alloy steel powder 4 for use.
Alloy element X Concentration range A (mass%)
Al 0.05 to 0.6
Si 0.1 to 1.5
P 0.05 to 0.3
Ti 0.05 to 0.4
V 0.05 to 1.0
Cr 0.2 to 10
Zn 0.1 to 5
Sn 0.1 to 1.5
W 0.1 to 5
Even if the content of the alloying element X as a pre-alloy exceeds the upper limit value, the effect of improving the hardenability does not change so much. On the contrary, the compression of the alloy steel powder 4 for powder metallurgy is reduced, which is not preferable. It is also disadvantageous from an economic point of view. On the other hand, when alloy steel powder 4 for powder metallurgy having a content of alloying element X as a pre-alloy is less than the lower limit is formed and sintered to obtain a sintered body, quenching treatment (for example, carburizing treatment and quenching) is performed thereafter. However, since the hardenability is low, a ferrite phase is easily generated in the sintered body. Therefore, it becomes difficult to increase the strength of the sintered body by heat treatment.

As described above, the iron-based powder 1 contains the alloying element X in a pre-alloyed form, and a powder metallurgy is obtained by diffusing and attaching the Y-containing powder 2 to the surface of the iron-based powder 1 or by attaching a binder. Alloy steel powder 4 for use. Due to this diffusion adhesion and binder adhesion, a high concentration portion in which the alloy element Y is not less than the following concentration B is formed in the surface layer portion of the iron-based powder.
Alloy element Y Concentration B (mass%)
Al 1
Si 2
P 0.5
Ti 0.5
V 2
Cr 13
Zn 7
Sn 2
W 5
As the alloy elements X and Y used in the present invention, an element that generates an α phase having a large diffusion coefficient even at a high temperature of about 1000 ° C. at a certain concentration or more in the Fe-M system is selected. According to the research by the inventors, Si, P, Ti, V, Cr, Zn, Sn, and W. Therefore, in the present invention, these elements are used as alloy elements X and Y. These alloy elements may be used alone or in combination of two or more.

  By sintering a compact using an alloy steel powder 4 for powder metallurgy in which a Y-containing powder 2 is adhered to the surface of an iron-based powder 1 prealloyed with the alloying element X of the present invention, between the particles of the iron-based powder 1 The alloying element Y has a high concentration in the sintered neck portion. For this reason, it is considered that an α phase is generated in the sintered neck portion, and as a result, sintering is promoted, pores are refined, and the sintered neck portion is strengthened. And it is thought that by controlling the diffusion adhesion amount of the alloy element Y within the scope of the present invention, the sintered neck portion is strengthened and the strength of the sintered body is improved.

The sintered neck portion is a portion where the sintering reaction starts at the initial stage of sintering, and specifically, a portion where the pressure-formed alloy steel powders 4 for powder metallurgy are close to each other. FIG. 5 is a sectional view conceptually showing the sintered neck portion 7. In FIG. 5, only the sintered neck portion related to the alloy steel powder 4 for powder metallurgy in the center in FIG. 5 is shown.
As explained above, since the alloy steel powder contains a small amount of elements contained in the iron-based powder as a pre-alloy, the hardness of the alloy steel powder is suppressed to a low level, and the alloy steel powder is highly compressed by compression molding. A compact with a density is obtained. In addition, since the alloy element Y is segregated at a high concentration on the surface of the iron-based powder particles (that is, a high concentration portion of Y is formed), when sintering the alloy steel powder compact, The α phase is formed on the contact surface. As a result, bonding between alloy steel powders by sintering is promoted.

As a state of the high concentration portion of the alloy element Y suitable in the present invention, a region where the concentration of the alloy element Y is equal to or higher than the above-described concentration B exists in an area ratio of 1% to 50% with respect to the alloy steel powder cross-sectional area. It is preferable that the average content of the alloy element Y satisfies the following range.
Alloy element Y Average content (% by mass)
Al 0.05 〜 2
Si 0.05 〜 6
P 0.05 〜 2
Ti 0.05 〜 2
V 0.05 to 3
Cr 0.05 to 20
Zn 0.05 to 5
Sn 0.05 to 8
W 0.05 〜 5
That is, the region where the concentration of the alloy element Y is equal to or higher than the concentration B is remarkably excellent in the effect of promoting the generation of the α phase and the sintering. The frequency with which the high concentration part of the element Y exists increases remarkably. If this region exceeds 50%, the sintering promoting effect tends to saturate, and it is effective to set the upper limit to 50% in order to avoid unnecessary reduction in cost and compressibility. A more preferred upper limit is 30%. The concentration of the alloy element Y in this region may be 100% by mass.

Whether or not the above-mentioned high concentration part state of the alloy element Y is satisfied is determined by analyzing the particle cross section of the alloy steel powder (select a cross section in which the diameter of the cross section is within ± 10% of the average particle diameter) by EPMA, This can be confirmed by measuring a region where the concentration of the alloy element Y is equal to or higher than a predetermined value and calculating the area by image analysis. In calculating the area, it is recommended to analyze 100 or more particle cross sections.
In addition, it is considered that the high concentration phase 5 is not sufficiently generated when the diffusion adhesion amount of the alloy element Y is less than the lower limit value. On the other hand, if the upper limit value is exceeded, the high concentration phase 5 becomes brittle, and it is considered that the strength decreases.

  Next, it is preferable that the fine particles of the Y-containing powder 2 are uniformly attached to the surface of the iron-based powder 1. When the powder is not uniformly attached, it is easy to fall off from the surface of the iron-based powder 1 when the alloy steel powder 4 for powder metallurgy is pulverized after the adhesion treatment or during transportation. Easy to increase. When sintering a molded object from the alloy steel powder of such a state, it exists in the tendency for sintering not to be accelerated | stimulated effectively. Therefore, in order to increase the fatigue strength of the sintered body, it is preferable to uniformly attach the Y-containing powder 2 to the surface of the iron-based powder 1 and reduce the free Y-containing powder generated by dropping or the like.

  In addition, when the particle size of the Y-containing powder 2 is 20 μm or less on average, the strength is particularly good. This is because when the particle size of the Y-containing powder 2 exceeds 20 μm on average, a coarse high-concentration phase 8 as shown in FIG. 4 is easily generated, sintering is not promoted, and pores are not refined. it is conceivable that. Therefore, the average particle size of the Y-containing powder 2 is preferably 20 μm or less. On the other hand, the average particle size of the Y-containing powder 2 is preferably 1 μm or more from the viewpoint of workability. The average particle size of the powder containing the alloying element Y is determined by measuring the particle size distribution by the laser diffraction / scattering method in accordance with JIS standard R1629 (1997 edition). Shall be used.

The following can be used as other raw materials.
Ni-containing powder or Cu-containing powder may be attached to the iron-based powder 1 as a reinforcing element. In that case, Ni-containing powder or Cu-containing powder may be added prior to the heat treatment and binder adhesion shown in FIG.
Graphite (or other carbon-containing powder may be used) is effective in increasing strength and fatigue strength, and is added prior to pressure forming to add graphite powder, etc. to a carbon equivalent of about 0.1 to 1.0% by mass (alloy after mixing) It is preferable to add and mix by mass ratio to steel powder, the same applies hereinafter). In addition, MnS: about 0.1 to 1% by mass can be added as an alloy powder to be mixed before pressure forming. These alloy powders may be adhered to the surface of the iron-based powder in order to prevent segregation, but diffusion adhesion is not suitable from the viewpoint of cost, and the use of a binder is preferred. In addition, the described component range is mass% with respect to the total mass of the alloy steel powder and alloy powder after mixing. After all, it is preferable to use only the Y-containing powder 2 as the alloy to be adhered.

The impurities contained in the iron-base powder and alloy steel powder include C: about 0.02% by mass or less, O: about 0.2% by mass or less, N: about 0.004% by mass or less, S: about 0.03% by mass or less. It is done. Impurities do not necessarily require a lower limit, but the industrial reduction limits (rough values) are described below. C: 0.001 mass%, O: 0.02 mass%, N: 0.0001 mass%, S: 0.001 mass%.
Mn contained in the iron-based powder 1 as a prealloy is preferably 0.5% by mass or less based on the mass of the alloy steel powder 4 for powder metallurgy. If the Mn content as the prealloy exceeds 0.5 mass%, the particles of the iron-based powder 1 become hard and the density is difficult to increase during molding. Moreover, since Mn has a strong affinity for oxygen, oxidation during sintering or grain boundary oxidation during gas carburization occurs, and fatigue strength is reduced. Therefore, Mn contained in the iron-based powder 1 as a prealloy is preferably 0.5% by mass or less. More preferably, it is 0.3 mass% or less.

Since Mn has a slight reinforcing effect, it may be intentionally included within the above range, but there is no need to provide a lower limit for reasons of material. However, the industrial lower limit considering the manufacturing cost is about 0.04% by mass.
The balance excluding the components described above is preferably iron.
Next, conditions suitable for producing a sintered body using the alloy steel powder for powder metallurgy of the present invention will be described.

  In the press molding, a powdery lubricant may be mixed. It is also preferable to apply or adhere a lubricant to the mold. For any purpose, metal lubricants such as zinc stearate, amide waxes such as ethylene bisstearamide, and the like can be suitably used as the lubricant. In the case of a lubricant to be mixed, the amount is preferably 0.1 to 1.2 parts by mass with respect to 100 parts by mass in total of the alloy steel powder for powder metallurgy and the alloy powder.

The pressure molding is preferably performed at a temperature of about 400 to 1000 MPa and a temperature of room temperature (about 20 ° C.) to about 160 ° C. The mold may be lubricated during pressure molding.
Sintering is preferably performed at about 1100 to 1300 ° C., but it is particularly preferable to sinter at 1160 ° C. or lower, which is possible with a mesh belt furnace that is inexpensive and can be mass-produced. More preferably, the sintering temperature is 1140 ° C. or lower. Further, the sintering is preferably performed at a temperature of 1120 ° C. or higher. Of course, other furnaces such as a tray pusher type sintering furnace may be used.

The obtained sintered body can be subjected to strengthening treatment such as carburizing quenching, bright quenching, induction quenching, carbonitriding treatment, etc., if necessary. The strength is improved as compared with the case of no treatment. When quenching or the like, a tempering process may be further performed.
In addition, what is necessary is just to give each reinforcement | strengthening process according to a conventional method. In the case of carburizing and quenching, it is preferable to quench after carburizing at a carbon potential of about 0.6 to 1.2 and a temperature of about 800 to 950 ° C. (both water quenching and oil quenching are possible). The carbon potential represents the carburizing ability of the atmosphere in which the steel is heated, and is the carbon concentration (mass%) on the surface of the steel when the carburizing temperature reaches equilibrium with the atmosphere of the gas used for carburizing.

For bright quenching, for example, the method and conditions described in paragraph [0031] of JP-A-2001-181701 are suitable.
In the induction hardening, it is preferable to perform induction hardening (both water quenching and oil quenching are possible) after induction heating so that the surface layer portion has a temperature of about 850 to 1100 ° C.
In carbonitriding, the carbon potential is about 0.6 to 1.2%, and the atmosphere is about 3 to 10% (volume fraction) of ammonia gas. After carbonitriding at about 750 to 950 ° C, quenching (water quenching, oil quenching) Any are possible).

  The components of the obtained sintered body are preferably C: 0.6 to 1.2% by mass, O: 0.02 to 0.15% by mass, and N: 0.001 to 0.7% by mass. Components other than C, O, and N are almost the same as the composition of the mixed powder before pressure forming (alloy steel powder for powder metallurgy and alloy powder mixed therewith).

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the mixed powder for powder metallurgy according to the present invention and its application are not limited to the following examples.
[Example 1]
Molten steel containing the alloy elements shown in Nos. 1 to 33 in Tables 1 and 2 was sprayed by a water atomizing method to obtain an iron-based powder as atomized.

When the alloy element is diffused and deposited, the alloy element powder is added to the iron-based powder at a predetermined ratio, mixed for 15 minutes in a V-type mixer, and then heat-treated in a hydrogen atmosphere with a dew point of 30 ° C (retention temperature 875 ° C). , Holding time 1 hr), and alloy steel powder for powder metallurgy was manufactured by diffusing and adhering the alloy element-containing powder on the surface of the iron-based powder.
A sample was taken from the alloy steel powder for powder metallurgy, and the amount of alloy contained in each sample was measured. The results are as shown in Table 1. In addition, the average particle diameter of any alloy steel powder for powder metallurgy was in the range of 70 to 90 μm.

Here, the particle size of the iron-based powder is determined according to the sieving test method described in JIS standard Z8815 (1994 version), and the average particle size at which the integrated sieving percentage (mass basis) is 50% is averaged. The particle size was taken.
In addition, the remaining structure of the obtained alloy steel powder is iron and inevitable impurities (C: 0.001 to 0.010 mass%, S: 0.008 to 0.012 mass%, N: 0.0006 to 0.0018 mass%, O: 0.09 to 0.2 mass%) It is.

The prealloy amount (mass%), the average content of alloy elements (mass%), and the diffusion adhesion amount (mass%) shown in Tables 1 and 2 are all values relative to the mass of the alloy steel powder for powder metallurgy.
Sample Nos. 1-4, 8-13, 21, 32 are examples in which the amount of pre-alloy and the amount of diffusion diffusion of the alloy satisfy the scope of the present invention. Samples Nos. 27 to 35 are examples in which the amount of alloy diffusion is outside the range of the present invention, and Samples Nos. 22 to 26 are examples in which the amount of pre-alloy is outside the range of the present invention.

Next, after the mold for pressure molding is heated to 130 ° C., lithium stearate is sprayed onto the mold using the Nordson apparatus disclosed in Japanese Patent Laid-Open No. 2002-327204, and the inner surface of the mold is sprayed. Charged and adhered.
Further, to these alloy steel powders for powder metallurgy, graphite was added in the amounts shown in Tables 1 and 2, and 0.8 parts by mass of lithium stearate was added and mixed for 15 minutes with a V-type mixer. Thereafter, it was heated to 130 ° C., filled into a mold, and pressure-molded at a pressure of 686 MPa to produce a tablet-like molded product having a length of 55 mm, a width of 10 mm, and a thickness of 10 mm.

The tablet-like molded body was sintered to obtain a sintered body. In the sintering process, the RX atmosphere (N ₂ -32 vol% H ₂ -24 vol% CO- 0.3 vol% CO _2), the sintering temperature 1130 ° C., and a sintered time of 20 minutes. After processing the obtained sintered body into a round bar tensile test piece with a parallel part diameter of 5 mm, gas carburizing at a carbon potential of 0.8% (holding temperature 870 ° C, holding time 60 minutes) and quenching (60 ° C, oil quenching) ) And tempering (200 ° C., 60 minutes). About the component of the sintered compact, the amount of C of the whole increased a little because carbon of the surface layer became 0.75-0.8 mass%. Further, the amount of O slightly decreased to a range of 0.05 to 0.12% by mass, and the amount of N slightly increased to a range of 0.01 to 0.02% by mass. The other components were almost the same as the raw material composition.

The density (Mg / m ³ ) and tensile strength (MPa) of these sintered bodies were measured. The results are also shown in Tables 1 and 2.
Comparing the surface pressure fatigue strength between the inventive example and the comparative example, the inventive example was 1200 to 1400 MPa, while the comparative example was 1000 to 1100 MPa. Therefore, if the alloy steel powder for powder metallurgy of the present invention is used, the tensile strength of the sintered body can be increased.

[Example 2]
Molten steel containing the alloy elements shown in Nos. 34 to 55 in Tables 2 and 3 was sprayed by a water atomizing method, then reduced in a hydrogen atmosphere, and further crushed to produce an iron-based powder. Metal powder or ferroalloy powder is added to this iron-based powder as alloy element-containing powder at a specified ratio, and 0.8 mass% of zinc stearate is added as a binder together with graphite, Cu powder and Ni powder, and heated to 140 ° C. The mixture was mixed for 15 minutes while adhering a metal powder to the surface of the iron-based powder to obtain an alloy steel powder for powder metallurgy. In addition, the addition amount (mass%) of zinc stearate is a ratio with respect to the total mass (namely, mass of alloy steel powder for powder metallurgy) of iron-base powder and Mo metal powder.

The remaining composition of the obtained alloy steel powder for powder metallurgy is the same as in Example 1.
After forming this alloy steel powder for powder metallurgy at a pressure of 686 MPa at room temperature, the same steps from sintering to tempering as in Example 1 were performed to produce a sintered body, and the density and tensile strength were measured. did. The results are as shown in Tables 2 and 3.
Sample Nos. 34 to 46 are examples in which the amount of pre-alloy and the addition amount of metal powder satisfy the scope of the present invention, Sample Nos. 51 to 54 are examples in which the addition amount of metal powder is outside the scope of the present invention, sample Nos. 47 to 50 are examples in which the amount of pre-alloy is outside the scope of the present invention.

  When the inventive example and the comparative example were compared, the density of the sintered body showed an equivalent value, but the tensile strength of the inventive example was superior.

It is sectional drawing which shows typically the example of the alloy steel powder used with the mixed powder for powder metallurgy of this invention, (a) is an example in which the Y containing powder has kept the original form, (b) is the M containing powder. It is an example of being crushed. It is a block diagram which shows the example of the manufacturing process of the alloy steel powder for powder metallurgy of this invention. It is sectional drawing which shows typically the typical example of the network structure | tissue of a sintered compact. It is sectional drawing which shows typically the typical example of the structure | tissue of the sintered compact in which the high concentration phase coarsened. It is sectional drawing which shows a sintering neck part typically.

Explanation of symbols

1 Iron-based powder 2 Y-containing powder (part of high concentration part)
3 Part to be contacted 4 Alloy steel powder 5 High concentration phase 6 Low concentration phase 7 Sintering neck 8 Coarse high concentration phase

Claims (4)

On the surface of the iron-based powder containing alloy element X, which is one or more of Al, Si, P, Ti, V, Zn, Sn and W, as a pre-alloy and the balance Fe and unavoidable impurities , An alloy steel powder for powder metallurgy to which a powder containing an alloy element Y which is one or more of Al, Si, P, Ti, V, Cr, Zn and Sn is attached, The prealloy amount (mass%) of the alloying element X in the powder is Al: 0.05 to 0.6, Si: 0.1 to 1.5, P: 0.05 to 0.3, Ti: 0.05 to 0.4, V: 0.05 to 1.0 , Zn : 0.1 to 5, Sn: 0.1-1.5, W: 0.1-5, and the average content (mass%) of the alloy element Y is Al: 0.05-2, Si: 0.05-6, P: 0.05-2, Ti: 0.05-2, V: 0.05-3, Cr: 0.05-20, Zn: 0.05-5, Sn: 0.05-8 were satisfied, and the concentration (mass) of the alloying element Y in the surface layer of the iron-based powder was satisfied. %) Is Al: 1 or more, Si: 2 or more, P : 0.5 or more, Ti: 0.5 or more, V: 2 or more, Cr: 13 or more, Zn: 7 or more, Sn: 2 is the following high concentration unit for powder metallurgy alloy steel powder, characterized in that there is.   2. The alloy steel powder for powder metallurgy according to claim 1, wherein the powder containing the alloying element Y is diffusion-attached.   The alloy steel powder for powder metallurgy according to claim 1, wherein a binder containing the powder containing the alloy element Y is attached. 3. The alloy steel powder for powder metallurgy according to claim 2, wherein the high-concentration part is present in a range of 1 to 50% of a cross-sectional area of the alloy steel powder for powder metallurgy.

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